AN3959 datasheet(28/65 Pages) STMICROELECTRONICS

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Design guidelines for schematic and PCB layout

AN3959

28/65

Doc ID 022081 Rev 3

Design guidelines for schematic and PCB layout

6.1

Schematic

6.1.1

Criteria for selection of components

●

Absolute maximum rating: STA381BWS VCC = 27 V

●

Bypass capacitor 100 nF in parallel to 1 µF for each power VCC branch. Preferable

dielectric is X7R.

●

Coil saturation current compatible with the peak current of application

6.1.2

Decoupling capacitors

For the decoupling capacitor(s), one decoupling system can be used with 2 capacitors per

channel. The decoupling capacitors must be as close as possible to the IC pins, in order to

avoid parasitic inductance with the copper wire on the PC board.

6.1.3

Output filter

Figure 27.

Output filter (BTL)

The key function of a snubber network is to absorb energy from the reactance in the

power circuit. The purpose of the snubber RC network is to avoid unnecessary high

pulse energy such as a spike in the power circuit which is dangerous to the system.

The snubber network allows the energy (big spike) to be transferred to and from the

snubber network in order for the system to work safely.

The purpose of the main filter is to cut off the frequency above the audible range of

20 kHz, which is mandatory in order to have a clean amplifer response. The main filter

is designed using the Butterworth formula to define the cutoff frequency.

The purpose of the damping network is to avoid the high-frequency oscillation issue on

the output circuit. The damping network allows the THD to be improved and also allows

avoiding the inductive copper on the PCB route when the system is working at high

frequency with PWM or PCM.

C98

470n

C105

100n

C101

100n

C95

100n

C89

100n

C90

330p

C99

1000p

C103

1000p

L13

22u

L11

22u

C91

1000p

R37

6.2

R34

6.2

R36

IN x A

IN x B

CO N2

SNUBBER

Main Filter

Dumping Network

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